/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package javax.servlet.jsp.tagext;

/**
 * Information on the scripting variables that are created/modified by a tag (at
 * run-time). This information is provided by TagExtraInfo classes and it is
 * used by the translation phase of JSP.
 * 
 * <p>
 * Scripting variables generated by a custom action have an associated scope of
 * either AT_BEGIN, NESTED, or AT_END.
 * 
 * <p>
 * The class name (VariableInfo.getClassName) in the returned objects is used to
 * determine the types of the scripting variables. Note that because scripting
 * variables are assigned their values from scoped attributes which cannot be of
 * primitive types, &quot;boxed&quot; types such as
 * <code>java.lang.Integer</code> must be used instead of primitives.
 * 
 * <p>
 * The class name may be a Fully Qualified Class Name, or a short class name.
 * 
 * <p>
 * If a Fully Qualified Class Name is provided, it should refer to a class that
 * should be in the CLASSPATH for the Web Application (see Servlet 2.4
 * specification - essentially it is WEB-INF/lib and WEB-INF/classes). Failure
 * to be so will lead to a translation-time error.
 * 
 * <p>
 * If a short class name is given in the VariableInfo objects, then the class
 * name must be that of a public class in the context of the import directives
 * of the page where the custom action appears. The class must also be in the
 * CLASSPATH for the Web Application (see Servlet 2.4 specification -
 * essentially it is WEB-INF/lib and WEB-INF/classes). Failure to be so will
 * lead to a translation-time error.
 * 
 * <p>
 * <B>Usage Comments</B>
 * <p>
 * Frequently a fully qualified class name will refer to a class that is known
 * to the tag library and thus, delivered in the same JAR file as the tag
 * handlers. In most other remaining cases it will refer to a class that is in
 * the platform on which the JSP processor is built (like J2EE). Using fully
 * qualified class names in this manner makes the usage relatively resistant to
 * configuration errors.
 * 
 * <p>
 * A short name is usually generated by the tag library based on some attributes
 * passed through from the custom action user (the author), and it is thus less
 * robust: for instance a missing import directive in the referring JSP page
 * will lead to an invalid short name class and a translation error.
 * 
 * <p>
 * <B>Synchronization Protocol</B>
 * 
 * <p>
 * The result of the invocation on getVariableInfo is an array of VariableInfo
 * objects. Each such object describes a scripting variable by providing its
 * name, its type, whether the variable is new or not, and what its scope is.
 * Scope is best described through a picture:
 * 
 * <p>
 * <IMG src="doc-files/VariableInfo-1.gif" alt="NESTED, AT_BEGIN and AT_END
 * Variable Scopes"/>
 * 
 * <p>
 * The JSP 2.0 specification defines the interpretation of 3 values:
 * 
 * <ul>
 * <li> NESTED, if the scripting variable is available between the start tag and
 * the end tag of the action that defines it.
 * <li> AT_BEGIN, if the scripting variable is available from the start tag of
 * the action that defines it until the end of the scope.
 * <li> AT_END, if the scripting variable is available after the end tag of the
 * action that defines it until the end of the scope.
 * </ul>
 * 
 * The scope value for a variable implies what methods may affect its value and
 * thus where synchronization is needed as illustrated by the table below.
 * <b>Note:</b> the synchronization of the variable(s) will occur
 * <em>after</em> the respective method has been called.
 * 
 * <blockquote> <table cellpadding="2" cellspacing="2" border="0" width="55%"
 * bgcolor="#999999" summary="Variable Synchronization Points"> <tbody>
 * <tr align="center">
 * <td valign="top" colspan="6" bgcolor="#999999"><u><b>Variable
 * Synchronization Points</b></u><br>
 * </td>
 * </tr>
 * <tr>
 * <th valign="top" bgcolor="#c0c0c0">&nbsp;</th>
 * <th valign="top" bgcolor="#c0c0c0" align="center">doStartTag()</th>
 * <th valign="top" bgcolor="#c0c0c0" align="center">doInitBody()</th>
 * <th valign="top" bgcolor="#c0c0c0" align="center">doAfterBody()</th>
 * <th valign="top" bgcolor="#c0c0c0" align="center">doEndTag()</th>
 * <th valign="top" bgcolor="#c0c0c0" align="center">doTag()</th>
 * </tr>
 * <tr>
 * <td valign="top" bgcolor="#c0c0c0"><b>Tag<br>
 * </b></td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, AT_END<br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * </tr>
 * <tr>
 * <td valign="top" bgcolor="#c0c0c0"><b>IterationTag<br>
 * </b></td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, AT_END<br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * </tr>
 * <tr>
 * <td valign="top" bgcolor="#c0c0c0"><b>BodyTag<br>
 * </b></td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<sup>1</sup><br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<sup>1</sup><br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, NESTED<br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, AT_END<br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * </tr>
 * <tr>
 * <td valign="top" bgcolor="#c0c0c0"><b>SimpleTag<br>
 * </b></td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff"><br>
 * </td>
 * <td valign="top" align="center" bgcolor="#ffffff">AT_BEGIN, AT_END<br>
 * </td>
 * </tr>
 * </tbody> </table> <sup>1</sup> Called after <code>doStartTag()</code> if
 * <code>EVAL_BODY_INCLUDE</code> is returned, or after
 * <code>doInitBody()</code> otherwise. </blockquote>
 * 
 * <p>
 * <B>Variable Information in the TLD</B>
 * <p>
 * Scripting variable information can also be encoded directly for most cases
 * into the Tag Library Descriptor using the &lt;variable&gt; subelement of the
 * &lt;tag&gt; element. See the JSP specification.
 */

public class VariableInfo {

	/**
	 * Scope information that scripting variable is visible only within the
	 * start/end tags.
	 */
	public static final int NESTED = 0;

	/**
	 * Scope information that scripting variable is visible after start tag.
	 */
	public static final int AT_BEGIN = 1;

	/**
	 * Scope information that scripting variable is visible after end tag.
	 */
	public static final int AT_END = 2;

	/**
	 * Constructor These objects can be created (at translation time) by the
	 * TagExtraInfo instances.
	 * 
	 * @param varName
	 *            The name of the scripting variable
	 * @param className
	 *            The type of this variable
	 * @param declare
	 *            If true, it is a new variable (in some languages this will
	 *            require a declaration)
	 * @param scope
	 *            Indication on the lexical scope of the variable
	 */

	public VariableInfo(String varName, String className, boolean declare,
			int scope) {
		this.varName = varName;
		this.className = className;
		this.declare = declare;
		this.scope = scope;
	}

	// Accessor methods

	/**
	 * Returns the name of the scripting variable.
	 * 
	 * @return the name of the scripting variable
	 */
	public String getVarName() {
		return varName;
	}

	/**
	 * Returns the type of this variable.
	 * 
	 * @return the type of this variable
	 */
	public String getClassName() {
		return className;
	}

	/**
	 * Returns whether this is a new variable. If so, in some languages this
	 * will require a declaration.
	 * 
	 * @return whether this is a new variable.
	 */
	public boolean getDeclare() {
		return declare;
	}

	/**
	 * Returns the lexical scope of the variable.
	 * 
	 * @return the lexical scope of the variable, either AT_BEGIN, AT_END, or
	 *         NESTED.
	 * @see #AT_BEGIN
	 * @see #AT_END
	 * @see #NESTED
	 */
	public int getScope() {
		return scope;
	}

	// == private data
	private String varName;
	private String className;
	private boolean declare;
	private int scope;
}
